Voyager 2 beams back tantalizing scenes of Uranus

January 22, 1986

By Robert C. CowenStaff writer of The Christian Science Monitor

Pasadena, Calif.

Here at NASA's Jet Propulsion Laboratory (JPL), TV monitors let reporters share a scene that amazes astronomers. Sometimes the huge disk of a virtually unknown planet dominates the picture. Then the bright arc of one of the planet's rings bisects the screen.

Voyager 2 is closing in on Uranus. And a world that astronomers have known only as a fuzzy little disk is coming ever more sharply into view.

Excitement runs high in the room where scientists of the Voyager imaging team study the primary display screens. As deputy project scientist Ellis D. Miner notes, ``We always have people looking over our shoulders . . . trying to see something that hasn't been seen before.''

At this writing, the score on such discoveries was seven new small moons, and counting. More moons may well pop into view as Voyager's increasingly detailed images reveal new features of the Uranian system. The planet has nine known rings. These are so sharply defined that mission scientists expect to find small moons within the ring system. The gravity of these so-called shepherd moons would keep ring particles in line. The moons discovered so far lie just outside the rings and probably don't exert much shepherding influence.

Even the estimated size of these small moons, announced earlier this month, may change as Voyager's TV cameras view them more closely. Preliminary estimates of their diameters have been in the range of 20 to 45 miles, depending on the particular moon. But there are indications that the moons may prove to be somewhat larger than these early estimates imply.

Uranus does have five larger, previously known, moons -- Miranda, Ariel, Umbriel, Titania, and Oberon. The new satellites have been found between Miranda's orbit and the outermost of the nine rings -- the epsilon ring. Scientists expect to see much detail on these moons. But Voyager was still too far away to begin to show it.

Voyager is beginning to see more detail in the planet's rings and on its surface. But the view was not yet clear enough at this writing for scientists to identify what they are beginning to see. But the view is sharpening rapidly.

Launched on Aug. 20, 1977, Voyager 2 has already inspected Jupiter (July 9, 1979) and Saturn (Aug. 25, 1981). It was designed to do no more than this and already is well beyond its five-year nominal lifetime. Nevertheless, JPL officials say the spacecraft is working well. They expect its equipment to continue to function during this ``bonus'' planetary survey.

Voyager is racing toward its Uranian rendezvous at a little better than 40,000 miles an hour. It's due to pass within 50,600 miles of the planet's cloud tops at 10 a.m. PST Friday. During that close encounter, scientists expect to learn more about the Uranian system in a quarter of a day than they have learned in the time since Sir William Herschel discovered the planet on March 13, 1781.